Application Of Fiber Bragg Grating Sensor In The Monitoring Of Seabed Excess Pore Water Pressure

Seabed geological disaster-related research has increasingly become a hot topic under the background of urgent need to recognize and study the ocean, and "Transparent Ocean" strategic plan proposed by Academician Wu Lixin. The monitoring of seabed pore water pressure, which is an important parameter in seabed geological disasters, is obviously of great significance. Now, conventional sensors is difficult to applied to the seabed excess pore pressure monitoring due to its shortcomings, and FBG sensors are more widely used due to its immunity to electromagnetic interference, corrosion resistance, electrical insulation, high sensitivity and low cost, and good compatibility to general fiber etc. The development of differential pressure sensor of excess pore water pressure play a crucial role to seabed geological disaster monitoring because it can be directly measured the deep seabed excess pore water pressure.Around the applied research of FBG sensor in the monitoring of seabed excess pore water pressure, this paper was carried out by the following several aspects.(1) The research status of seabed (excess) pore water pressure theory, monitoring, and FBG sensors is summarized, and the principles and advantages of FBG sensors are detailed.(2) A Fiber grating excess pore water pressure sensor is developed, and the corrosion resistance and pressure resistance of the fiber material are tested. The results indicate that, the optical fiber material has stable wavelength values under high pressure and corrosive conditions, and the coated fiber grating is more stable than the bare optical fiber grating material. So, the coated fiber material can completely satisfy the material requirement of the deep-sea excess pore water pressure sensor under the condition of high pressure and corrosion.(3)The matching excess pore water pressure sensor with fiber grating and monitoring systems are designed and developed, and the sensitivity tests are carried out on the probes of excess pore water pressure sensor with fiber grating, and flume experiments are simulated the undersea environment to verify its practicality. The results indicate that, the monitor results of fiber grating excess pore water pressure sensor can not only match the results of conventional piezoresistive sensor, but also reflect its good stability and high sensitivity characteristics, and verified that the application of FBG sensor in excess pore water pressure monitoring is a successful attempt.(4) The experimental data are analyzed comprehensibly, and the theory is validated by the result. The excess pore water pressure of "seabed" is generated by applying artificial waves and artificial vibration load, and is monitored by conventional pore water piezoresistive pressure sensors, pressure sensors and earth FBG sensors monitor. The conclusions related to the dynamic response of elastic seabed are verified by the monitoring results:the magnitude of the seabed excess pore water pressure decreases with increasing depth, and effective stress amplitude under the surface of the shallow seabed area reaches its maximum; compared with the seabed surface wave pressure, there are usually phase lag phenomenon on pore water pressure and effective stress.It should be recognized that the present paper is just a try work in the initial stage, a lot of research needs to be carried out urgently, with the actual monitoring needs, improving the technology and equipment of FBG sensors in excess pore water pressure monitoring, making the technology from experiment room to practical application, a huge boost will be bring to the research and production.